Water-absorptive resins have been widely applied to, for example, sanitary absorbent materials such as paper diaper and sanitary napkin, agricultural water retention materials and industrial materials. Examples of these conventional water-absorptive resins include starch derivatives such as alkali metal salts of starch/acrylic acid graft copolymer, saponified starch/ acrylonitrile graft copolymer and saponified starch/ acrylamide graft copolymer; cellulose derivatives such as carboxymethyl cellulose, saponified cellulose/ acrylonitrile graft copolymer and alkali metal salts of cellulose/acrylic acid graft copolymer; polyacrylic acid derivatives such as alkali metal polyacrylates; and polyvinyl alcohol derivatives such as alkali metal salts of polyvinyl alcohol/acrylic acid graft copolymer and polyvinyl alcohol/maleic anhydride graft copolymer. Each of these resins is formulated into a crosslinked powder in order to achieve a shape-retention characteristic after absorbing water.
Recently the range of the application of these water-absorptive resins has been more and more increasing and it is required to formulate these resins not only into a powder but also into various forms including film, sheet and fiber. However, every conventional water-absorptive resin is a crosslinked material and thus has a poor thermoplasticity, which makes it significantly difficult to mold the same into a film, a sheet or fibers.
On the other hand, it has been attempted to mold a conventional water-absorptive resin into a film or fibers by, for example, employing a composition of a water-absorptive resin with a polyolefin resin such as polyethylene, ethylene/vinyl acetate copolymer, ethylene/ acrylic acid copolymer or ethylene/propylene copolymer or rubber (cf. Japanese Laid-Open Patent Application Nos. 75747/76, 33032/81 and 145151/82). However, the composition thus obtained has some disadvantages such that the water absorption ratio is lowered and that the water-absorptive resin is significantly eliminated after absorbing water, though the aimed moldability is achieved.